Vitamin D in the fight against COVID-19; Hype vs. Reality

As many suppositions have been circulating concerning COVID-19 for months now, and one of them is the correlation between vitamin D and COVID-19. There are currently no FDA approved medications, vaccines, or other treatments for the prevention or treatment of the novel coronavirus disease, but this has not discouraged speculation about potential treatment options. People are becoming prudently watchful to find ways of protecting themselves from Covid-19, and thus curiosity in unapproved approaches has stepped up. Vitamin D is one prevalent, contentious supplement that has recently gripped the attention of the public. While studies have reported the connection between vitamin D and COVID-19, it is a mystifying scenario. Some scientists believe that while vitamin D plays a role in immune function, it might not have a significant impact on how your body reacts to Covid-19. Still, preliminary, non-peer-reviewed studies suggested a potential link between vitamin D deficiency and worsening outcomes of COVID-19. Recent reports have indicated vitamin D deficiency could increase the risk of COVID-19 mortality, and we should consider taking vitamin D supplements to protect ourselves. Although it is an essential vitamin for optimal health,  it is also a “fat-soluble” vitamin, which means an excess of it can deposit inside the body and can cause kidney damage.

There may be something, at least in theory, to the arguments made in relation to COVID-19, and all those claims refer to our immune system. Calcitriol, the active vitamin D hormone, helps to regulate both innate and adaptive immune systems, our first and second lines of defense against pathogens, and the lack of vitamin D is associated with immune dysregulation. Several ways in which calcitriol affects the immune system are directly relevant to our virus-defense capability. Calcitriol triggers the production of cathelicidin and other naturally occurring defensin antivirals that can prevent the virus from replicating and entering a cell. Calcitriol may also increase the number of a particular type of immune cell (CD8 + T cells), which plays a critical role in clearing acute viral infections in the lungs. It also suppresses pro-inflammatory cytokines, molecules secreted from immune cells that promote inflammation. Some scientists have suggested that vitamin D can help alleviate the “cytokine storm” typically seen in the worst cases of COVID-19. This could be important in severely ill Covid-19 patients where excessive damage to the lung can result from an inflammatory “cytokine storm” , although further research is needed to examine this claim. Interestingly, the latest report published in the BMJ  Nutrition, Prevention and Health, found no link between vitamin D supplements and COVID-19 prevention or treatment. In addition, due to health risks, they warned against the over-supplementation of vitamin D without medical supervision.

There are recent reports linking vitamin D deficiency with worse COVID-19  outcomes. But other underlying risk factors, such as heart disease, also impact the severity of the disease and hence,  making it difficult to draw conclusions. There is also some evidence that vitamin D can play a role in preventing certain respiratory infections. While this evidence stems from systematic reviews of randomized trials, it has many limitations, including heterogeneous definitions of respiratory infections, populations studied, and vitamin D deficiency interventions. The research team led by Northwestern University performed a statistical analysis of data from hospitals and clinics around China, France, Germany, Italy, Iran, South Korea, Spain, Switzerland, UK, and the United States. Researchers noted that patients from countries with high COVID-19 mortality rates, such as Italy, Spain, and the United Kingdom, had lower levels of vitamin D compared to patients in countries not so severely affected. This does not mean that everyone, especially those without an established deficiency, needs to start hoarding supplements.“Although I think it is important for people to know that vitamin D deficiency may play a role in mortality, we do not need to force vitamin D on everyone.  This needs further study, and I hope our work in this area will generate interest. The data may also illuminate the mortality mechanism, which could lead to new therapeutic targets if verified”, said Vadim Backman, principal investigator at Northwestern.

Guyatt, one of the pioneers of “evidence-based medicine,” says this reflects a more significant problem we see with COVID-19: an epidemic of speculation about therapeutic solutions and preventive measures based on preliminary results of studies which have not produced conclusive evidence.

As a research scientist with expertise in vaccine immunology, cancer biology, and cancer immunotherapy, I would be meticulous to draw a conclusion after reading the recent research on vitamin D supplementation in COVID-19 patients. Before prescribing vitamin D3 supplements for treating or preventing COVID-19 infection, I would endorse the need for more persuasive evidence from well-masked controlled trials to determine substantial positive impact. Specific emphasis should be placed on vitamin D, not as a ‘magic bullet’ against but as part of a healthy lifestyle strategy to ensure that communities are nutritionally in the best place possible. Furthermore, before we go any further, there is no evidence to support the idea that vitamin D has beneficial value for people who are infected with the virus or are exposed. Supplementing the sunshine vitamin may well be a good idea for many people, especially those over the age of 65 and/or people who do not get out during daylight hours but still need a supplementary consultation with their doctors.

Until future large and well-designed studies have been performed, we do not know precisely the effect of vitamin D in COVID-19. Yet,  upping your intake is the least crackpot of all the dietary concepts out there.

Dr Ajaz Ahmad Bhat is a research scientist at Sidra Medicine, Doha, Qatar and former postdoctoral research fellow at Vanderbilt University Medical School, Nashville, TN, USA.